Control system for a tilt tray sorter

ABSTRACT

A speed control system for a sorting conveyor for transporting objects and unloading objects at one or more unloading stations adjacent the conveyor. Each of the tilting conveyor carts includes a trailer frame base, a carrying tray for holding the objects and a two-axis tiltable support apparatus for supporting the carrying tray above the trailer frame base and for allowing tilting of the carrying tray towards at least one side of the conveyor to unload objects into unloading stations on at least one side of the conveyor. The conveyor system includes a plurality of selectively energized linear induction motors for driving the train along the conveyor track. A speed control system including a fixed-frequency, variable-voltage transformer is connected to a portion of the linear induction motors for varying the speed of the train.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-in-Part of U.S. applicationSer. No. 08/632,012, filed Apr. 15, 1996, now U.S. Pat. No. 5,836,436issued Nov. 17, 1998.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates generally to package sorting conveyorsand, more particularly, to a control system for such a conveyor system.

(2) Description of the Related Art

Conveyor systems having a number of individual carrying carts have beencommonly used for many years to carry and sort packages or other items,such as mail. For example, U.S. Pat. No. 5,054,601 to Sjogren et al.discloses a package sorting conveyor comprised of a train of tilt traycarriers coupled in tandem to form a continuous loop. Each carrierincludes a pivotally mounted tilt tray normally maintained in an uprightposition. The carriers are moved around the loop by a series of motorsspaced around the loop. Branching out from the loop are outfeed chutesor the like for receiving packages from the carriers. When a particularcarrier holding a particular package to be sorted reaches a selectedoutfeed chute, an actuator tilts the tray to dump the package into theoutfeed chute. Another example of a typical package sorting conveyor isdisclosed in International PCT Application Number PCT/DK90/00047 ofKosan Crisplant A/S.

One significant disadvantage of conventionally designed package sortingconveyors is that conventional conveyor carriers laterally tilt only ona horizontal axis parallel to the direction of conveyor travel. Whilethis accomplishes the objective of dumping the package from the carrierinto an outfeed chute or the like, the package is often roughly tumbledor rolled, sometimes damaging the package's contents. One reason forthis is that the packages typically are unloaded from the carrier whilestill traveling forward at the same speed as the conveyor. Thus,packages tend to slam into a forward retaining wall of the outfeed chutebefore sliding down the chute. Another problem with conventionallaterally tilting conveyors is that because the packages are movingforward at full speed when they are unloaded into the outfeed chute, theoutfeed chute must be relatively wide so that packages do not miss thechute and fall off the conveyor past the chute. This often unnecessarilyincreases the overall size of the conveyor system.

U.S. Pat. No. 4,744,454 and an improvement thereto, U.S. Pat. No.5,086,905, both to Pölling, disclose previous attempts to remedy thisproblem of rough handling by conventional laterally tilting conveyorcarriers. Both of these patents to Pölling disclose a conveyor elementfor a package conveyor that includes a tilting carrier tray mounted tobe rotatable about two swivel axes. A first swivel shaft extendsobliquely downward from the underside of the carrying tray and is inturn connected at an angle to the end of a second swivel shaft extendingobliquely upwards from a base support part of the conveyor element.Together, the two swivel shafts form a “V” that points in the directionof conveyor travel. Both of the swivel shafts lie in the vertical planeof symmetry of the conveyor element when the carrier tray is disposed inits upright position.

Because the carrier tray of Pölling rotates about two oblique axes, thecarrier tray can be tilted not only lateral on a horizontal axis, but ismoved through a geometrically complex spatial reorientation duringpackage discharge. This allows for more gentle placement of a package onan outfeed chute than can be accomplished using conventional conveyortrays that laterally tip on only a horizontal axis. The Pölling conveyorelement more gently handles the packages by imparting some degree ofrearward velocity to the packages as they are discharged, which, whenadded to the forward velocity of the conveyor system, results in thepackages' forward velocity during discharge being less than that of theconveyor system itself.

However, the conveyor elements of both of Pölling's patents are undulycomplicated and intolerant of manufacturing discrepancies. In fact, thesecond Pölling conveyor element (U.S. Pat. No. 5,086,905) was inventedin an attempt to simplify the original design disclosed in the firstPölling patent (U.S. Pat. No. 4,744,454), which had proved to be tooexpensive and complicated to manufacture efficiently. As a result ofthis complexity and cost, the Pölling devices have not enjoyedsignificant commercial acceptance and success.

One solution to this problem is shown in co-pending U.S. applicationSer. No. 08/632,012, filed Apr. 15, 1996, now U.S. Pat. No. 5,836,436issued Nov. 17, 1998, the entire disclosure hereby incorporated byreference.

Another problem which is more recent has arisen from the movement of theindustry from chain driven sorters to linear induction motor (LIM)driven sorters. LIM's are extremely quiet and have fewer moving partswhich require maintenance. However, such systems are not trouble freeand have a tendency to overheat when run at lower speeds. It is nowbelieved that the conventional practice of using an AC inverter tocontrol by varying frequency produces transients which contribute tothis heating problem which occurs predominately in linear inductionmotors. In addition, in such “chain-less” systems it has proven moredifficult to accurately determine the speed and position of the trayssince there is no physical connection between the trays and the motor.

Thus, there remains a need for a new and improved control system for atilting conveyor system that substantially eliminates the heatingproblem when the LIM is run at slower speeds while, at the same time,accurately determines the speed and position of the trays.

SUMMARY OF THE INVENTION

The present invention is directed to a control system for a sortingconveyor for transporting objects and unloading objects at one or moreunloading stations adjacent the conveyor. Generally, the sortingconveyor includes: a conveyor track; a train of the tilting conveyorcarts connected end-to-end; and a power source for moving the conveyorcarts on the conveyor track. Each of the tilting conveyor carts includesa trailer frame base. The trailer frame includes a roller structure forengaging the conveyor track, a driven member responsive to the powersource, and a hitch mechanism for connecting each tilting conveyor cartto an adjacent conveyor cart. The conveyor cart also includes a carryingtray for holding the objects and a two-axis tiltable support apparatusfor supporting the carrying tray above the trailer frame base and forallowing tilting of the carrying tray towards at least one side of theconveyor to unload objects into unloading stations on at least one sideof the conveyor.

The two-axis tiltable support apparatus includes an upper supportstructure joined to the carrying tray, a lower support structure joinedto the trailer frame base, and an angled pivot structure connecting theupper support structure to the lower support structure along a pivotaxis, wherein the pivot axis is disposed at an angle to a line of travelof the sorting conveyor so as to impart two axial components to thetilting of the carrying tray.

A tilting mechanism tilts the carrying tray on the tiltable supportapparatus to thereby unload objects into one of the unloading stationsadjacent the conveyor.

According to the present invention, the conveyor system includes aplurality of selectively energized linear induction motors for drivingthe train along the conveyor track. A speed control system including afixed-frequency, variable-voltage transformer is connected to a portionof the linear induction motors for varying the speed of the train.

In the preferred embodiment, the speed control system includes a fixedfrequency AC electrical power supply and a fixed-frequency,variable-voltage transformer connected to the power supply. Apreselected number of the linear induction motors are connected directlyto the fixed frequency AC electrical power supply and the remaininglinear induction motors are connected to the transformer. A voltagecontroller is connected to the transformer for receiving a speed settinginput signal and sending a variable voltage signal to the transformer toreduce its voltage output, thereby controlling the speed of the cart. Aspeed sensor assembly detects the speed of the train and providing anoutput signal representative of the speed to the speed control system.

Accordingly, one aspect of the present invention is to provide a packagesorting conveyor system of the type having at least one conveyor cartmovable along a continuous conveyor track and at least one unloadingstation. The conveyor system includes: (a) a conveyor track; (b) a trainof conveyor carts connected end-to-end and movable along the conveyortrack; (c) a plurality of selectively energized linear induction motorsfor driving the train along the conveyor track; and (d) a speed controlsystem including a fixed-frequency, variable-voltage transformerconnected to a portion of the linear induction motors for varying thespeed of the train.

Another aspect of the present invention is to provide a speed controlsystem for a package sorting conveyor system of the type having at leastone conveyor cart movable along a continuous conveyor track and at leastone unloading station and a plurality of selectively energized linearinduction motors for driving the train along the conveyor track. Thespeed control system includes: (a) an electrical power supply; (b) atransformer connected to the power supply; (c) a preselected number ofthe linear induction motors connected directly to the power supply; (d)a preselected number of linear induction motors connected to thetransformer; and (e) a voltage controller connected to the transformerfor receiving a speed setting input signal and sending a variablevoltage signal to the transformer to reduce its voltage output, therebycontrolling the speed of the cart.

Still another aspect of the present invention is to provide a packagesorting conveyor system of the type having at least one conveyor cartmovable along a continuous conveyor track and at least one unloadingstation. The conveyor system includes: (a) a conveyor track; (b) a trainof conveyor carts connected end-to-end and movable along the conveyortrack; (c) a plurality of selectively energized linear induction motorsfor driving the train along the conveyor track; (d) a speed controlsystem including a fixed-frequency, variable-voltage transformerconnected to a portion of the linear induction motors for varying thespeed of the train, the speed control system including: (i) anelectrical power supply; (ii) a transformer connected to the powersupply; (iii) a preselected number of the linear induction motorsconnected directly to the power supply; (iv) a preselected number oflinear induction motors connected to the transformer; and (v) a voltagecontroller connected to the transformer for receiving a speed settinginput signal and sending a variable voltage signal to the transformer toreduce its voltage output, thereby controlling the speed of the cart;and (e) a speed sensor assembly for detecting the speed of the train andproviding an output signal representative of the speed to the speedcontrol system.

These and other aspects of the present invention will become apparent tothose skilled in the art after a reading of the following description ofthe preferred embodiment when considered with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a package sorting conveyorconstructed according to the present invention;

FIG. 2 is front, elevational view of a single tilting conveyor cart ofthe package sorting conveyor and the power source of the conveyor;

FIG. 3 depicts a train of trailer frame structures of the conveyorcarts, as seen from the top, but with the tiltable support apparatusesand the carrying trays of the conveyor carts removed for clarity;

FIG. 3A depicts a top view of an axle caster that holds a roller wheelon one of the conveyor carts;

FIG. 3B is a cross-sectional view of the axle caster and roller wheel ofFIG. 3A, taken along lines 3B—3B;

FIG. 4 is an elevational side view of one of the tilting conveyor cartsof the present invention;

FIG. 5 is a sectional side view of a tilting conveyor cart, taken alonglines 5—5 of FIG. 2, which shows the tiltable support apparatus and theangled pivot structure of the tilting conveyor cart of the invention;

FIG. 5A is a geometric depiction of the conveyor cart pivot axis andconveyor line of travel as they relate to three-dimensional X,Y,Zspatial coordinates;

FIG. 6 is a top view of the train of carts of the package sortingconveyor of the present invention;

FIG. 6A shows the train of carts of FIG. 6, but with one of the carts inits tilted position and unloading a package onto an unloading stationbeside the sorting conveyor track;

FIG. 7 is a rear view of the tilting conveyor cart taken along lines 7—7of FIG. 4 with the track rails and the roller structure omitted forclarity, which shows the conveyor cart in its upright, horizontalposition and an end view of the speed sensor assembly;

FIG. 7A shows the tilting conveyor cart of FIG. 7 in its tiltedposition;

FIG. 8 is a side elevational view of the pull-down mechanism of theinvention with its switch in an open position as it captures a passingroller wheel on a conveyor cart actuating arm;

FIG. 8A is another side view of the pull-down mechanism, except with theroller wheel traveling through the descending ramp and the switch in itsclosed position;

FIG. 9 is a top view of the pull-down mechanism with the switch in itsopen position, capturing a passing roller wheel;

FIG. 9A is another top view of the pull-down mechanism, except with theroller wheel traveling through the descending ramp and the switch in itsclosed position;

FIG. 10 is a top view of the push-up mechanism;

FIG. 10A is a side view of the push-up mechanism;

FIG. 11 is a schematic block diagram of a control system for the LIMmotors constructed according to the present invention;

FIG. 12 is a side view of the speed sensor assembly; and

FIG. 13 is a schematic flowchart of the cart locating system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, like reference characters designate likeor corresponding parts throughout the several views. Also in thefollowing description, it is to be understood that such terms as“forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly”, andthe like are words of convenience and are not to be construed aslimiting terms.

Referring now to the drawings in general and FIG. 1 in particular, itwill be understood that the illustrations are for the purpose ofdescribing a preferred embodiment of the invention and are not intendedto limit the invention thereto. As seen in FIG. 1, a sorting conveyor,generally designated 10, is shown constructed according to the presentinvention for transporting and sorting packages 11 or other objects. Thesorting conveyor 10 comprises a train of individual carts 20, connectedend to end, which preferably form an endless loop around aclosed-circuit conveyor track 12. Alternately, the conveyor carts 20 ofthe invention could be used singly or as part of a finite train.

The package sorting conveyor 10 generally includes four majorsub-assemblies: a conveyor track 12; a power source 70; the train oftilting conveyor carts 20, which are moved along the conveyor track 12by the power source 70; and a tilting mechanism 80 for tilting theconveyor carts 20 to discharge packages 11 therefrom. Typically, anynumber of unloading stations or outfeed chutes 18, which are adjacentthe package sorting conveyor 10 on one or both sides thereof, receivethe packages 11 discharged from the sorting conveyor 10 and carry thepackages to waiting storage bins, trucks, etc. Packages may be manuallyplaced on the conveyor carts 20 or may be delivered to the sortingconveyor 10 via infeed chutes 17 or the like.

The conveyor track 12 includes two parallel rails 14 and may be built toconform to the layout of any warehouse, shipping center, distributioncenter, or the like. Best seen as resembling the track of a rollercoaster, the conveyor track 12 may be substantially horizontal or mayascend and descend. The conveyor track rails 14 may lie in the samehorizontal plane, or one may be higher than the other, such as would bethe case in a banked curve in the track 12. Banked curves are greatlyadvantageous because they allow the conveyor carts 20 to move around acurved conveyor track 12 at a much greater speed without spillingpackages 11 than on a flat track. Preferably, the rails 14 are generallytubular, again similar to a roller coaster, and are supported by railsupport members 16 only on the outwardly facing edges of the rails. Therails 14 may be round or rectangular in cross-section. Rectangularcross-section is preferred since it has been found that round railscause the roller wheels to wear somewhat in their center because theload is not as well distributed as when rectangular rails are utilized.

The power source 70 of the sorter conveyor 10, which is shown in FIG. 2,is preferably a vertically oriented linear induction motor (LIM). Thevertically oriented LIM 70 of the present invention is an improvementover previously designed LIM's, which typically are horizontallydisposed below the conveyor track. Conventional LIM's also usuallydepend on the presence of a heavy steel plate in each conveyor cart toprovide a pathway through which electromagnetic flux from theelectromagnetic coil of the LIM passes, thereby driving the carts alongthe track. This causes two problems. The first problem is with excessiveweight of the conveyor cart train resulting from the presence of thesteel plates.

The second problem is with maintaining the proper distance between theelectromagnetic coil of the LIM and the conveyor cart, because gravitycoupled with magnetic attraction constantly try to pull the conveyorcart downwardly towards the electromagnetic coil. Magnetic attraction,which attracts the cart towards the electromagnetic coil, accounts forapproximately ten percent of the force generated by the electromagneticcoil. Longitudinal thrust, which drives the conveyor cart train aroundthe conveyor track, accounts for approximately ninety percent of theforce generated by the electromagnetic coil. While the ten percentmagnetic attractive force is relatively weak compared to the ninetypercent longitudinal thrust force, it is still enough to pull theconveyor cart into contact with the electromagnetic coil, especiallywhen assisted by gravity in a configuration where the LIM ishorizontally disposed below the conveyor track. If the conveyor cart isdrawn into contact with the electromagnetic coil, the carts are frozenin place because even the ninety percent longitudinal thrust componentof the LIM's total force cannot overcome the friction created by thecontacting surfaces magnetically held together. This contact andresulting conveyor failure is normally prevented by maintaining adistance between the conveyor cart and the electromagnetic coil withwhatever apparatus is used to support the train of conveyor cartsmoveably on the conveyor track. However, as parts wear, the distancebetween the conveyor carts and the electromagnetic coil is reduced untilcontact and resulting conveyor cart seizure is likely to occur.

The LIM 70 of the present invention solves both of these problems in twodifferent ways. First, the conventional steel flux plate is replacedwith a second electromagnetic coil 72 b, which is preferably identicalto, but out-of-phase with, a first electromagnetic coil 72 a. Eachelectromagnetic coil thus performs the function of the steel plate forthe other electromagnetic coil, i.e. electromagnetic coil 72 a providesa flux path for electromagnetic coil 72 b and vice versa. Elimination ofthe conventional steel plate reduces the weight of and, accordingly, theenergy required to move the train of conveyor carts 20.

Second, the LIM 70 is vertically oriented so that a driven fin 36, whichis attached to the bottom of each conveyor cart 20, hangs downwardly inbetween the two electromagnets 72 a,b. Composed of aluminum or otherconductive metal, the vertical fin 36 preferably has swept-back front 36a and rear 36 b edges, as shown in FIG. 4, giving the fin 36 a generallyparallelogram shape. Vertically orienting the fin 36 and the LIM 70greatly reduces problems with maintaining proper spacing between the fin36 and the electromagnets 72 a,b, because gravity ceases to be a factorand because the two electromagnets 72 a,b, both attract the fin 36equally. This results in the fin 36 being easily maintained equidistantbetween the two electromagnets 72 a,b of the LIM 70 of the invention,thereby preventing the fin 36 from contacting one of the electromagnetsand being seized in place as described above.

The electromagnets 72 a,b are out-of-phase with respect to each other sothat the inductive force they create will flow in the same direction. Inother words, the electromagnets 72 a,b are electrically out-of-phasewhile physically opposed to each other so as to supplement each other'sinductive forces on the fin 36, instead of canceling each other out.This helps provide a consistent motive force on the train of conveyorcarts because longitudinal thrust remains constant even if the fin 36 ispulled slightly closer to one of the electromagnets 72 a,b of the LIM70. While the longitudinal thrust is thereby increased with respect tothe closer electromagnet, the longitudinal thrust with respect to themore distant electromagnet is proportionally decreased. Thus, totallongitudinal thrust in the direction or line of travel remains constanteven if the fin 36 wavers slightly from side to side. While a smalldegree of lateral fin movement may occur, the structure of the carts andthe opposing pull of the electromagnets 72 a,b prevent the fin frombeing pulled into contact with either electromagnet. The LIM 70ordinarily moves the train of conveyor carts 20 in one direction oftravel; however, it can also be reversed if necessary to run the sortingconveyor backwards.

Now turning to the train of tilting conveyor carts 20, each cart 20includes three major sub-assemblies, shown best in FIG. 2: a trailerframe structure 22, a generally horizontally disposed carrying tray 40for holding the packages 11, and a tiltable support apparatus 50 forsupporting the carrying tray 40 above the trailer frame structure 22 andfor allowing tilting of the carrying tray 40 towards either side of thesorting conveyor 10 to unload a package into one of the unloadingstations. Each cart 20 is built around a base trailer frame structure 22to which other components of each cart 20 are mounted. As shown in FIG.3, the trailer frame structure 22 includes a longitudinal base member 24that extends in the direction of conveyor travel 64 between the twoparallel rails 14. Preferably, the base member 24 is substantiallyequidistant from each rail 14.

A roller structure 26 for riding on the conveyor track 12 is mounted ona front end of the base member 24 and includes two laterally extendingroller wheel mechanisms 27, one for each rail 14. The reason for theoutboard placement of the rail supports 16 and the tubular shape of therails 14 becomes apparent upon examining the roller wheel mechanisms 27.Each roller wheel mechanism 27 includes three roller wheels: an upperroller wheel 30 a for riding on the top edge of the rail 14, a middleroller wheel 30 b for riding on an inside edge of the rail 14, and alower roller wheel 30 c for riding on the bottom edge of the rail 14.With this configuration, it is almost impossible for a cart 20 to jumpthe track 12, because a wheel is provided for each directional force(sideways, upward, and downward) that a cart 20 may encounter whentraveling along the track 12. Preferably, each roller wheel 30 a,b,c isconstructed of a somewhat resilient material such as polyurethane toprovide for smooth, quiet, relatively vibration-free operation of thesorter conveyor 10.

Referring now especially to FIGS. 3A and 3B, the structure of eachroller wheel mechanism 27 that holds the top wheel 30 a is shown ingreater detail. Each top roller wheel 30 a is retained by an axle caster28 that is preferably formed from extruded aluminum or the like. Theaxle caster 28 includes two forks 28 a and 28 b, one on each side of thewheel 30 a, and a bearing bore 28 c disposed at the juncture of the twoforks 28 a,b, which has an opening 28 d on one side so that the bearingbore 28 c communicates with the space between the forks 28 a,b. A pairof flange bearings 29 seated in the bearing bore 28 c are disposedaround an axle shaft 27 a extending from the roller structure 26.Preferably formed of “oilite” or other friction-reducing material, eachflange bearing 29 has the form of a top-hat bushing and includes acenter hole 29 a through which passes the axle shaft 27 a. The rollerwheel 30 a is held in place between the two forks 28 a,b by a bolt 31and nut 31 a. Preferably, the roller wheel 30 a includes a bearingstructure 30 d disposed around the bolt 31, which serves as an axlerunning through the center of the wheel 30 a.

The axle caster shown in FIGS. 3A and 3B represents an improvement overexisting axle casters that hold roller wheels. Due to wear, axle castersinevitably tend to become loose and allow the roller wheels to chatterback and forth, which would inhibit smooth, quiet, vibration-freeoperation of a sorting conveyor. However, previously designed axlecasters typically have a bearing around the axle shaft that must bepressed out when worn and replaced with a new bearing that must bepressed in. This requires a press in addition to more time and expensethan is desirable in a large sorting conveyor system.

The axle caster 28 of the present invention solves this problem byproviding that the flange bearings 29 can easily be slid into place byhand into the bearing bore 28 c without using a press. Then, toimmovably secure the flange bearings 29 inside the bearing bore 28 c,the forks 28 a,b are slightly flexed inwardly towards each other as thenut 31 a is tightened onto the bolt 31 to hold the wheel 30 a in place.The forks 28 a,b of the axle caster 28 are therefore formed minutelywider apart than would be necessary to merely hold the wheel 30 a. Whenthe forks 28 a,b are flexed inwardly towards each other by tighteningthe nut 31 a on the bolt 31, the opening 28 d of the bearing bore 28 cis closed somewhat and the bearing bore 28 c is itself slightlydistorted, securely retaining the flange bearings 29 therein. The flangebearings 29 themselves are, however, not significantly distorted and arefree to swivel back and forth on the axle shaft 27 a. Therefore, theflange bearings 29 can easily and immediately be replaced on-site whenworn, eliminating much down-time that would be required ifconventionally designed axle casters were used in the conveyor cart 20of the present invention.

Adjacent carts 20 in the train are connected together using hitchmechanisms 32. Each hitch mechanism 32 is shown in FIGS. 3 and 4 asincluding a front hitch 32 a mounted on the front end of the base member24 in front of the roller structure 26 and a rear hitch 32 b mounted onthe rear end of the base member. In the embodiment disclosed, each hitch32 a,b has a vertical throughbore, through which a hitch pin connector32 c is inserted. Preferably, the hitch mechanisms 32 are configured sothat the front hitch 32 a on a rearward cart is disposed overtop of therear hitch 32 b on a forward cart. In the alternative, the hitchmechanisms 32 may comprise a poly-directional spherical ball jointmechanism similar in structure to an automotive trailer hitch. In eithercase, friction between hitch mechanism components is preferably reducedby, for example, lining the hitch components with TEFLON® or otherrelatively friction-free material.

To prevent adjacent conveyor carts 20 from separating should the hitchmechanism 32 accidentally break or become uncoupled, an auxiliary cartconnector 34 is preferably connected between the trailer framestructures 22 of adjacent carts 20. In the preferred embodiment, theauxiliary cart connector 34 is a metal cable or lanyard, although otherhigh-tensile strength materials could be used. In the embodimentdepicted, the auxiliary cart connector 34 is an approximately {fraction(3/16)}th inch thick metal cable connected to adjacent trailer framestructures 22 with metal mounting connectors 34 a.

The primary reason that metal is the preferred material for theauxiliary cart connector 34, besides its strength, is so that theauxiliary cart connector 34 will also serve as a continuous electricalconnector between adjacent carts 20. Electrical continuity between carts20 is important because of static electricity build-up while the carts20 are traveling around the conveyor track 12. However, because theroller wheels 30 a,b,c are preferably formed of polyurethane (anelectrical insulator) and because the components of the hitch mechanism32 are preferably coated with TEFLON® (also an electrical insulator),electrical continuity between adjacent carts 20 would not otherwise beeffectively achieved. By electrically connecting the carts 20, staticcharges can be bled off from the train, which is important for safetyand operational considerations. Thus, the auxiliary cart connector 34serves two important purposes: first, it physically attaches twoadjacent conveyor carts 20 and prevents them from becoming completelyseparated should the hitch mechanism 32 fail; second, it enableselectrical continuity among all of the conveyor carts 20 in the train.

The configuration of the conveyor cart 20 of the present invention, withits forwardly mounted roller structure 26, particularly structured hitchmechanism 32, and swept-back fin 36 is a significant improvement overpreviously designed conveyor carts. In conventional conveyor carts, theroller structures are typically mounted at the rear end of the trailerframe and the rear hitch is disposed overtop of the forward hitch. Whena hitch mechanism breaks or becomes accidentally uncoupled with this oldconfiguration, the result is that the forward end of the trailer framedrops below the conveyor track and is pushed over underlying structuresor the floor, leading to inevitable damage to the sorter conveyor.

With the present design, even without the auxiliary connector cable 34,only the rear end of the trailer frame structure 22 will drop below theconveyor track 12 upon accidental disengagement of the hitches 32 a,b orupon breakage of the hitch mechanism 32. Therefore, instead of the frontend 36 a of the driven fin 36 digging into the floor or underlyingstructures below the conveyor, as is the case with prior art conveyors,the driven fin 36 will simply be dragged with relatively minimal damageshould one of the hitches 32 break or become accidentally uncoupled. Ifan auxiliary connector cable 34 is attached between two adjacent carts20 that break apart, the connector cable 34 will limit the distance thatthe rear end of the trailer frame structure 22 will drop, furtherlimiting damage.

Mounted atop the trailer frame structure 22 of each conveyor cart 20 isthe tiltable support apparatus 50, which supports the carrying tray 40thereabove. As can best be seen in FIG. 5, the tiltable supportapparatus 50 generally includes three components: an upper supportstructure 52 joined to a bottom surface of the carrying tray 40, a lowersupport structure 58 centrally mounted atop the longitudinal base member24, and an angled pivot structure 60 pivotally connecting the lowersupport structure 58 to the upper support structure 52 along a pivotaxis 62.

In turn, the upper support structure 52 includes a front support member54 and a back support member 56. The lower support structure 58 ispreferably generally planar, lying in the vertical plane parallel to theconveyor line of travel 64, and includes an angled upper edge 58 a. Thepivot structure 60 preferably includes an axle 68 that runs eitherthrough or along the upper edge 58 a of the lower support structure 58and is connected to the front and back support members, 56, 58,respectively. Preferably, the axle 68 runs through lower regions of thefront and back support members 56, 58. As can be seen, the front supportmember 54 depends farther down from the carrying tray 40 than the backsupport member 56. While the lower support structure 58 is stationarilyfixed to the trailer frame 22, the axle 68 allows the upper supportstructure 52 to pivot along the pivot axis 62 of the pivot structure 60.

In an alternate embodiment of the tiltable support apparatus (notshown), the upper support structure 52 could also comprise, like thelower support structure 58, a generally planar member that lies in thevertical plane parallel to the conveyor line of travel 64. In this case,the angled pivot structure 60 could take on the form of a hingestructure joining together the two generally planar support structures52, 58.

The pivot axis 62 lies in a vertical plane parallel to the conveyor lineof travel, which is shown in the drawings as horizontal line 64.However, unlike conventional sorter conveyor tilting carts, the pivotaxis 62 of the conveyor cart 20 of the invention is disposed at an angleθ to the conveyor line of travel 64 so as to impart two axial componentsto the tilting of the carrying tray 40. Preferably, the pivot axis 62 isangled downwardly at an angle of approximately 20 to 45 degrees belowhorizontal in a forward direction. In the embodiment disclosed, thepivot axis 62 is angled downwardly 30 degrees. As can be seen in FIG. 5,the pivot axis 62 preferably intersects a plane occupied by the carryingtray 40 rearward of the center of the tray 40.

By disposing the pivot axis 62 at a downwardly directed angle θ insteadof parallel to the conveyor line of travel 64, two axial components areimparted to the tilting motion of the carrying tray 40. The first axialcomponent of the tray's tilting motion is lateral tipping on ahorizontal axis parallel to the conveyor line of travel 64. The secondaxial component of the tray's tilting motion is rotating around avertical axis 66 perpendicular to the conveyor line of travel. Thus,while the tray only tilts along a single, angled pivot axis 62, theoverall motion of the tray 40 as it tilts includes two axial components.

The tilting motion of the tray may also be described usingthree-dimensional X, Y, and Z-axis spatial coordinates, as shown in FIG.5A, wherein the Y-axis is parallel to the conveyor line of travel 64,the X-axis extends horizontally perpendicular to the line of travel 64,and the Z-axis extends vertically perpendicular to the line of travel64. In the present invention, tilting of the tray 40 includes a Y-axisand a Z-axis component, for as shown in FIG. 5A the pivot axis 62intersects the Y and Z axes. Specifically and for illustrative purposesonly, using the preferred 37.5 degree downward angle θ of the pivot axis62, it can be appreciated that the ratio of Y-axis motion to Z-axismotion is 60:30. In other words, with a 30 degree angle θ, the tray 40laterally tips somewhat farther than it rotates. If the angle θ of thepivot axis 62 is increased to 45 degrees below horizontal, then the traywill tilt and rotate equally.

As shown in FIGS. 6 and 6A, one effect of this two-axis tilting of thecarrying tray 40 is that a side 44 b of the tray that is tilteddownwardly also rotates rearwardly relative to the cart 20, as shown inFIG. 6A by line 46 a. Side 44 d of the tray, which is tilted upwardly,rotates forwardly relative to the cart 20, as shown in FIG. 6A by line46 b. In the preferred embodiment, in which the pivot axis 62 intersectsthe plane occupied by the tray 40 rear-of-center, the front side 44 a ofthe tray 40 rotates a greater distance around the vertical axis 66 thanthe back side 44 c of the tray 40, upon tilting of the tray 40. As shownin FIG. 6A, the bisecting center line of the tray 40 rotates farther atits forward end from the horizontal line of travel 64 than at itsrearward end. Thus, front side rotation line 48 a follows a longer arcthan back side rotation line 48 b. By rearwardly rotating whichever sideof the tray 40 is being tilted downwardly, some rearward velocity isimparted to packages 11 as they are being discharged from the cart 20 ofthe invention into an unloading station 18. Thus, packages aredischarged at a lower velocity relative to the unloading station thanthe velocity of the train of conveyor carts as a whole. This enables thepackages to be discharged into a narrower chute than could beaccomplished using a conventional conveyor cart. Additionally, becausethe packages are slowed down somewhat as they are discharged, there isless potential for damage to occur.

As can be seen in the drawings, the tray 40 may also include upwardlyangled lateral wings 42 to help prevent packages 11 from accidentallyfalling off the tray 40. These wings 42 also decrease the angle of theslope created when the tray 40 is tilted, which helps with gentlehandling of the packages 11 as they are discharged from the cart 20.

When a carrying tray 40 reaches a particular destination unloadingstation 18, the tilting mechanism 80 tilts the carrying tray 40 to causea package 11 carried thereon to be discharged into the unloading station18. The tilting mechanism 80 generally includes components mounted oneach conveyor cart 20 and components associated with each unloadingstation 18. First is a pair of actuating arms 82 attached beneath eachcart's carrying tray 40 on opposite lateral sides thereof, one actuatingarm 82 on each side of the cart's tiltable support apparatus 50. Secondis a pull-down mechanism 90 immediately upstream from each unloadingstation 18. The pull-down mechanism 90, when activated, selectivelypulls down one of the actuating arms 82 and thereby pulls the respectiveside of the tray 40 downwardly and rearwardly into the biaxially tiltedposition described above. Third is a push-up mechanism 110 downstream ofthe unloading station 18, which pushes up the actuating arm 82 pulleddown by the pull-down mechanism 90 and thereby reorients the tray 40into its normal, upright position. Fourth is a locking structure 120,which locks the carrying tray 40 in the tilted position upon pullingdown of one of the actuating arms 82, and which also locks the carryingtray 40 in its normal, upright position upon pushing up of thatactuating arm 82.

Referring now to FIGS. 7 and 7A, each actuating arm 82 is pivotallyattached to the underside of one side of the carrying tray and ispreferably connected to the front and back support members, 54 and 56respectively, of the upper support structure 52. In the embodimentshown, the actuating arm 82 is attached to the front and back supportmembers by an angled pivot hinge axle 84 that runs through both supportmembers 54, 56 and through the upper end of the actuating arm 82. Theactuating arm 82 therefore pivots on a pivot axis 86 that is preferablyparallel to the pivot axis 62 of the tiltable support apparatus 50, asshown in FIG. 5. As can be seen from an examination of the drawings, theactuating arms 82 and their respective pivot axes 86 remainsubstantially in a vertical plane parallel to the conveyor line oftravel 64 when stationary and when being pulled down or pushed up.

Each actuating arm 82 also includes a roller wheel 88, which engages thepull-down and push-up mechanisms 90, 110, as will be described below.The roller wheel 88 is preferably mounted on the lower end of theactuating arm 82 on an outer surface 82 a thereof. It is conceivable,however, that the roller wheel 88 could be replaced with a frictionreducing slide block or other protrusion for engagement by the pull-downand push-up mechanisms 90, 110.

Seen in detail in FIGS. 8, 8A, 9, and 9A, a pull-down mechanism 90 isassociated with each unloading station 18 and is located beneath therail 14 running closest to the unloading station 18 on the upstream sidethereof, as indicated in FIG. 6A. The pull-down mechanism 90 includes adescending ramp 92 and a laterally pivoting switch 94 that, whenactuated, pivots open and directs the roller wheel 88 of a passingactuating arm 82 into the descending ramp 92. As can be seen in thedrawings, when the switch 94 is not actuated, the switch is in a closedposition parallel to the ramp 92, and the roller wheel 88 is free tobypass the switch and the descending ramp 92. However, when a particularpackage 11 arrives at its destination unloading station 18, the switch94 is automatically actuated so that it pivots open into the path of thepassing roller wheel 88, capturing the roller wheel 88. The roller wheel88 then rolls through the switch 94, causing the actuating arm 82 topivot outwardly somewhat, and into the descending ramp 92. As the rollerwheel 88 rolls through the switch 94, the roller wheel 88 engages aclosure flange 104 having a curved end 106 to thereby pivot the switch94 back to its closed position, as the roller wheel 88 exits the switch94 and enters the descending ramp 92. Next, the descending ramp 92forces the roller wheel 88 and the associated actuating arm 82downwardly so as to pull down one side of the tray 40, therebydischarging the package from the tray 40 into the unloading station 18adjacent the pull-down mechanism 90.

A computer controller (not shown) is used to track all packages 11moving on the conveyor 10 and to automatically actuate a switch 94 atthe appropriate time when a particular package 11 reaches itsdestination unloading station or outfeed chute 18. The computer is alsoconnected to the LIM 70 to control the movement of the conveyor trainand maintain a desirable rate of speed.

In a preferred embodiment of the switch 94, a biasing member 96, such asa coil spring, is used to constantly urge the laterally pivoting switch94 towards its open position. However, to prevent the switch 94 fromalways remaining open and thereby capturing every passing roller wheel88, a lock catch 98 is provided to hold the switch closed. The lockcatch 98 pivots on a horizontal pivot member 98 a between the normal,horizontal position shown in FIG. 8A, which holds the switch 94 closed,and the tilted position shown in FIG. 8, which allows the switch 94 toswing open. A catch 102 depending from the forward end of the switch 94engages an outboard side of the lock catch 98 as the switch is heldclosed. When the switch 94 is closed by the action of the passing rollerwheel 88 on the closure flange 104, the depending catch 102 slides overa slanted end 98 b of the lock catch 98 back into position on theoutboard side of the lock catch 98.

Beneath the forward end 98 c of the lock catch 98 opposite the slantedend 98 b is a vertically oriented solenoid 100, which is actuated by thecomputer controller. Upon receiving a short pulse of electricity fromthe computer controller, the vertical solenoid 100 pushes the forwardend 98 c of the lock catch 98 upwardly to pivot the lock catch 98 andrelease the depending catch 102 of the switch 94. The switch 94 is thenswung into its open position by the biasing spring 96, where it capturesthe next passing roller wheel 88.

After the carrying tray 40 has been tilted and a package carried thereonhas been discharged into an unloading station 18, the carrying tray isreoriented into its normal upright position by the push-up mechanism110. Seen best in FIGS. 10 and 10A, a push-up mechanism 110 isassociated with each unloading station 18 and is located beneath thetrack 12 adjacent the unloading station 18 on the downstream sidethereof, as indicated in FIG. 6A. Each push-up mechanism 110 includes anascending ramp 112 below the rail 14 adjacent the unloading station 18.The push-up mechanism 110 also includes a wedge-shaped frog 114 thatengages the roller wheel 88 on a pulled-down actuating arm 82 anddirects the roller wheel 88 into the ascending ramp 112. The frog 114 ispositioned low enough below the track 12 so that roller wheels 88 willbe engaged and directed into the ascending ramp 112 only if they havealready been pulled down by the pull-down mechanism 90. As the rollerwheel 88 is directed into the ascending ramp 112, the actuating arm 82is pivoted outwardly somewhat so that the outside edge 123 of thelocking flange 122 will disengage from the tilted position lockingchannel 127. To help pull the actuating arm 82 back into substantiallyvertical alignment after the locking flange 122 has slid over the slidesurface 130, the top of the ascending ramp 112 includes an inwardlyturned section 116.

Now turning to the locking structure 120 of the tilting mechanism 80, itcan be seen best in FIGS. 7 and 7A that the locking structure 120includes a pair of locking flanges 122, a pair of locking blocks 124mounted one each to the actuating arms 82, and a biasing member 134 forbiasing the actuating arms 82 inwardly into a locked position.Preferably, the locking flanges 122 laterally extend from both sides ofthe lower support structure 58 of the tiltable support apparatus 50,although they could also be mounted to the trailer frame structure 22.In the embodiment disclosed, the locking flanges 122 comprise generallyplanar steel plates having rollers 123 mounted to their outer edges 123.In an alternate embodiment, the rollers 123 could be eliminated and thelocking blocks 124 made of a low-friction material on which theroller-less outer edges of the locking flanges 122 could easily slide.

Each locking block 124 is mounted to an inner surface 82 a of theactuating arm 82 and includes two locking channels 126 and 134 separatedby a cammed section 130 having a generally convex outer surface. Thelower 126 of the two locking channels receives the roller 123 at theouter edge of the lateral locking flange 122 when the carrying tray 40is in its upright position. The upper 134 of the two locking channelsreceives the roller 123 when the carrying tray 40 is in its tiltedposition. As the tray 40 is tilted from one position to the other, theroller 123 rolls over the cammed section 130 interposed between the twolocking channels 126, 134. Preferably, the locking blocks 124 are madeof a wear-resistant material such as plastic, although other materialscould be used. The biasing member, which may be a spring 134, pulls theactuating arms 82 inwardly so as to engage the locking structure 120 byseating the locking flanges 122 in one of the locking channels 126, 134.

During tilting of the tray 40 by the pull-down mechanism 90, theactuating arm 82 being pulled down is pivoted outward slightly on thepivot axis 86 as the roller wheel 88 is captured by the switch 94 anddirected into the descending ramp 92. This outward pivoting of theactuating arm 82 causes the upright position locking channel 126 todisengage from the locking flange 122. Then, as the roller wheel 88 ispulled down by the descending ramp 92, the locking flange 122 rollsupwardly over the cammed section 130. Because of the curved, convexshape of the cammed section 130 of the locking block 124, the actuatingarm 82 remains substantially vertical as it is pulled down. This helpsprevent the roller wheel 88 from slipping out of the descending ramp 92of the pull-down mechanism 90. Eventually, the locking flange 122 isseated in the tilted position locking channel 134 as the wheel exits thedescending ramp 92 and the tray 40 reaches its fully tilted position.The degree to which the tray 40 is tilted in the fully tilted positioncan vary depending on the configuration of the locking blocks 124 andthe pull-down mechanism 90. However, in the embodiment disclosed, thetray 40 is tilted approximately 37.5 degrees from horizontal in thefully tilted position.

The biasing member 134 holds the tilted position locking channel 134 andthe locking flange 122 together while the cart 20 is moving past theunloading station 18, stabilizing the tray 40 in the tilted position.Then, when the downwardly pulled actuating arm 82 reaches the push-upmechanism, the arm 82 is pivoted outwardly by the wedge-shaped frog 114engaging the roller wheel 88. This outward pivoting causes the lockingflange 122 to disengage from the tilted position locking channel 134. Asthe roller wheel 88 moves up the ascending ramp 112, the locking flangerolls downwardly over the cammed section 130. As the inwardly turned topend 116 of the ascending ramp 112 pivots the actuating arm 82 back toits vertical orientation, the locking flange 122 seats in the uprightposition locking channel 126, where it is held in place through theaction of the biasing member 134.

The actuating arm 82 on the opposite side of the conveyor cart 20, whichis not being pulled down or pushed up at a particular unloading station18, simply rises and falls with the side of the tray 40 to which it isattached. The locking flange 122 on this side of the cart 20 simplyrolls over a flat section 132 of the locking block 124 below the uprightposition locking channel 126.

In an alternate embodiment (not shown) of the package sorting conveyor10 of the invention, the conveyor cart 20 could include a tiltablesupport apparatus having a pivot axis that is not angled downwardly butthat is generally parallel to the conveyor line of travel 64. In thiscase, the tilting motion of the carrying tray 40 would only have asingle axial component—lateral tipping on a horizontal axis parallel tothe conveyor line of travel 64. While package sorting conveyors having asingle-axis lateral tipping motion have been designed in the past, theydo not include the other inventive features of the present sortingconveyor 10 such as the vertically oriented LIM 70, the hitch mechanism32 and auxiliary cart connector 34, and the tilting mechanism 80 withits associated components.

Such single-axis conveyor carts would primarily be incorporated into thepackage sorting conveyor 10 of the present invention for use in sortingparticularly large packages that must be carried by two or more adjacentcarrying carts 20. In this case, the trays of the adjacent carts wouldbe simultaneously tilted as the carts reached an unloading station todischarge the package. This would also of course require an especiallywide outfeed chute as well as a pull-down mechanism adjacent theunloading station for each cart to be simultaneously tilted.

The reason that single-axis conveyor carts are especially useful forsorting large packages is that it has been found that this double (ortriple, etc.) unloading of particularly large packages using thetwo-axis carrying carts 20 of the present invention occasionallypresents difficulties due to the carrying trays 40 not being in the samespatial plane when they are both in their fully tilted positions.Therefore, for double unloading, it is preferable to use the alternate,single-axis embodiment of the conveyor cart.

Several configurations of the package sorting conveyor 10 may beemployed that utilize the alternate, single-axis conveyor carts fordouble unloading situations. A preferable configuration would comprisetwo adjacent single-axis carts for carrying a single large package. Asecond configuration would comprise a leading two-axis conveyor cart 20and a trailing single-axis cart. A third configuration would comprise aleading single-axis conveyor cart and a trailing two-axis conveyor cart20. As a whole, the package sorting conveyor 10 of the invention mayinclude both two-axis conveyor carts 20 as well as single-axis conveyorcarts interspersed among each other depending on a particular facility'sconveying and sorting requirements.

Referring now to FIG. 11, a control system for the LIM motors, generallydesignated 140, is shown constructed according to the present inventionaccording to this continuation-in-part application. In the preferredembodiment, the speed control system 140 for the conveyor sorter 10includes three subsystems: a voltage control system 140 that provides afixed frequency, variable voltage output to the LIM 70; a quick stopcontrol system; and a cart locating system.

According to this aspect of the invention, the speed of the conveyorsorter 10 is controlled by way of a feedback arrangement comprised of apower supply 142, a voltage controller 146 for controlling the voltageto approximately twenty percent (20%) of the LIM's 70 a, a transformer144 that receives an input from the voltage controller 146 and thatprovides a fixed frequency, variable voltage output to the LIM's 70 a,and a speed sensor assembly 170.

In the prior art, the speed of a conveyor sorter generally wascontrolled by varying the frequency of the electrical current to the LIMwith an AC inverter. It has been discovered, that this conventionalvariable frequency control system, however, tends to cause the LIM tooverheat. In the present invention, eighty percent of the LIM's 70 b arepowered by a direct electrical connection, operating at a constantfrequency of about 60 cycles per second. To the contrary, the prior artgenerally used a control system that varies the frequency of theelectrical current to all of the motors.

If, however, all of the LIM's 70 were powered by a direct connection,there would be no way to vary the frequency or the voltage of theelectric current to the LIM's 70 and, therefore, no way to vary thespeed of the sorter conveyor 10. Thus, in the present invention,approximately eighty percent (80%) of all the LIM's 70 b are powereddirectly from the AC power supply, and the remaining approximatelytwenty percent (20%) of the LIM's 70 a are powered by a transformer 144that is controlled by a voltage control system 146.

By decreasing the voltage to some of the LIM's 70 a, the motor torque isdecreased, slippage between the tray fin 36 and the motor increases andthe sorter conveyor 10 moves more slowly.

In operation as schematically shown in FIG. 11, the voltage controller146 receives a signal from a speed setting input 147, which receives thedesired speed of the conveyor sorter 10 from the operator. For example,a computer keyboard can be used for inputting the desired speed and acomputer monitor can be used to display the desired speed that has beeninputted. A speed sensor assembly 170 continuously measures the speed ofthe conveyor sorter 10, and provides a signal of the conveyor sorter 10speed to the voltage controller 146, which is continuously compared tothe speed setting input 147 for purposes of regulating the voltage ofthe current applied to the associated LIM's 70.

In the preferred embodiment, a speed sensor assembly 170 constructedaccording to the present invention comprises at least one pair ofU-shaped proximity switches 172 a,b that are attached below the conveyorframe and positioned adjacent to the passage of fin 36. The switches 172a,b are operable to detect the approximately one (1) inch gaps betweeneach aluminum fin 36 attached to the bottom of each conveyor cart 20 andwhich hangs downwardly in between the two electromagnets 72 a,b.

The centers of the proximity switches 172 a,b are mounted approximatelytwo (2) inches apart. As a conveyor cart 20 moves around the track 12,the proximity switches 172 a,b transmit a signal to a timer 178, whichmeasures the amount of time it takes the air gap in each aluminum fin 36to travel from the first proximity 172 a to the second proximity switch172 b. A speedometer 180 then calculates the speed of the conveyor cart20 and sends a signal 182 to the voltage controller 146, which thencompares the actual speed of the conveyor cart 20 to the set point. Thevoltage controller then sends a signal to the transformer 144 toincrease or decrease the voltage to the selected LIM's 70. Thisarrangement is shown in FIG. 12.

In the preferred embodiment, as many as 12 pairs of these sensors areused around the conveyor track and the speedometer 180 continuouslycalculates the speed of the conveyor carts 20 as each sensor is“tripped” by the gap between the carts.

In an alternative embodiment, a single sensor could be used to measurethe time between the end of one fin and the beginning of the next finand, if the length of each fin was known, the speed of the tray couldalso be calculated. However, it is believed that the preferredembodiment, using a pair of sensors spaced apart a fixed distance, wouldusually be more accurate since the measurement is made in only the timeit takes the gap to move about two inches instead of the time it wouldtake for an entire tray to pass a single sensor.

Under normal conditions, the sorter conveyor 10 is stopped by removingpower to all LIM's 70 and the sorter conveyor coasts to a stop. Thepresent invention, however, also includes a quick stop control system,which includes a contactor 150 and a quick stop activation switch 151.

In operation, if an emergency occurs, the operator of the sorterconveyor 10 activates the activation switch 151, the contactor 150“forward” opens, which removes the power from the voltage controlledLIM's 70 a and reverses the three-phase power to the directly poweredLIM's 70 b. By reversing the three phase power to the directly poweredLIM's 70 b, the stopping distance of the sorter conveyor isapproximately one-half of the stopping distance under normal conditions.

After the sorter conveyor 10 comes to a complete stop, the sorterconveyor 10 may reverse direction and move several inches along thetrack 12 until the casters 30 a mounted to the load bearing axle 28splay out in the turns of the track 12 and stop the backward movement ofthe sorter conveyor 10. In the preferred embodiment, a timer 152 removesall power to the directly powered LIM's 70 b after a predeterminedperiod of time after the operator activates the contactor 150.

In the preferred embodiment as shown in FIG. 13, a cart locator system154, also referred to as a tiploc system, constructed according to thepresent invention includes a retro-reflective strip 160 that is fixablysecured to each pull-down mechanism 90 at each chute and an uniquecarrying tray 40 that is arbitrarily designated as “tray one” 40 a. Alight source 156 and photocell 158 is secured directly to the “tray one”40 a and emits a continuous light focused down upon where the pull-downmechanism 90 is located.

In the prior art, the problem was as sortation systems became larger andlarger, it was becoming more and more difficult to locate a cart withrespect to firing a pull-down mechanism to tip the right cart and notone cart before or one cart after. For example, in a 1200 chutesortation conveyor each tray is fired off at one of 1200 tippers basedon a reference point. That is the computer lets tray 1 go 2014 inchesafter tray 1 passes the reference point and that is where the right tipand that tray should correspond to one another.

In the prior art, a database is built in the computer manually for eachtray and each location using two technicians each having awalkie-talkie. The sorter would be run at speed and the technicianswould try to see if the tipper was firing early or firing late, i.e.getting the wrong tray at that location! If the trays were on 22 inchcenters, 22 inches would be added or subtracted and the test would berun again depending on whether it was one tray early or one tray late.However, it could be that it was just getting or just missing a tray. Assystems have become larger, the problem has become larger too.

One alternative is to have intelligent tippers which are able toidentify each cart individually. However, this “multiplex” technique isvery expensive and, as shown during the 1995 start-up at the DenverAirport, can be extremely troublesome to get up and running.

In operation of the present invention, when “tray one” 40 a carrying thelight source 156 passes the pull-down mechanism location, theretro-reflective strip 160 reflects the light which is detected byphotocell 158, which is secured adjacent to the light source 156. Whenthe photocell 158 senses the reflected light, an electronics package 263located on tray one 40 a emits a radio frequency signal that is receivedby a receiver 264 which is mounted in close proximity to the sortercontrol system 265. This signal system is well-known in the art forsending a RF signal to a transmitter module at a remote location, suchas those found in a conventional burglar alarm system. This systemprovides for the sorter control system 265 to know the location of trayone 40 a at a precise moment in time.

Preferably, the trays, including “tray one” 40 a, referred to as theSmart Tray™, are run around the track a number of times thereforeautomatically building the database for each pull-down mechanism withrespect to the reference point without requiring several weeks to do so.For example, using the prior art technique it took 6 weeks tosynchronize 400 tippers. Significantly, the present invention requiredonly 1 day to synchronize 200 tippers.

Once the position of tray one 40 a has been determined, the position ofevery other device in the system can be determined as a function of thenumber of pulses received from the sensor 172 a,b because each pulse isproportional to distance. As tray one 40 a proceeds around the track,the sorter control system 265 counts the number of pulses it receivesfrom sensors 172 a,b. The control system upon receipt of the input fromtray one captures the current pulse count and places it in a list. Thefirst signal and captured count represents the distance to the firsttray, and so on respectively until a count is captured for everypull-down mechanism position.

Certain other modifications and improvements will occur to those skilledin the art upon a reading of the foregoing description. It should beunderstood that all such modifications and improvements have beendeleted herein for the sake of conciseness and readability but areproperly within the scope of the following claims.

We claim:
 1. A speed control system for a package sorting conveyorsystem of the type having at least one conveyor cart movable along acontinuous conveyor track and at least one unloading station and aplurality of selectively energized linear induction motors for drivingsaid train along said conveyor track, said speed control systemcomprising: (a) an electrical power supply; (b) a transformer connectedto said power supply; (c) a preselected number of said linear inductionmotors connected directly to said power supply; (d) a preselected numberof linear induction motors connected to said transformer; and (e) avoltage controller connected to said transformer for receiving a speedsetting input signal from a speed sensor and sending a variable voltagesignal to said transformer to vary its voltage output, therebymaintaining said cart substantially at a predetermined speed in responseto said speed sensor input signal for controlling the speed of saidcart.
 2. The apparatus according to claim 1, further including anemergency stopping system, said stopping system including means forreversing the direction of said linear induction motors.
 3. Theapparatus according to claim 2, wherein said emergency stopping systemincludes: an activation switch activated by the operator of said packagesorting conveyor system; a contactor connected to said activation switchfor removing power from said plurality of said selectively energizedlinear induction motors and for reversing phases of the power to saidplurality of selectively energized linear induction motors; and a timerfor removing all power to said plurality of selectively energized linearinduction motors after a predetermined time after the operator activatessaid activation switch.
 4. A package sorting conveyor system of the typehaving at least one conveyor cart movable along a continuous conveyortrack and at least one unloading station, said conveyor systemcomprising: (a) a conveyor track; (b) a train of conveyor cartsconnected end-to-end and movable along said conveyor track; (c) aplurality of selectively energized linear induction motors for drivingsaid train along said conveyor track; and (d) a speed control system,wherein said speed control system includes control means for maintainingsaid train substantially at a predetermined speed in response to anoutput signal representative of the speed of said train from a speedsensor, said speed sensor being adapted to detecting the speed andproviding said output signal to said speed control system, and afixed-frequency, variable-voltage transformer connected to a portion ofsaid linear induction motors for varying the speed of said train, saidspeed control system including: (i) an electrical power supply; (ii) atransformer connected to said power supply; (iii) a preselected numberof said linear induction motors connected directly to said power supply;(iv) a preselected number of linear induction motors connected to saidtransformer; and (v) a voltage controller connected to said transformerfor receiving a speed setting input signal and sending a variablevoltage signal to said transformer to vary its voltage output, therebycontrolling the speed of said cart.
 5. The apparatus according to claim4, wherein said speed sensor assembly includes: at least one proximityswitch for detecting first and second preselected points on anindividual cart spaced apart a predetermined distance; a timer connectedto said switch for measuring the amount of time between when saidproximity switch detects the first preselected point and when saidproximity switch detects the second preselected point and providing anoutput signal representative of said amount of time; and a speedometerconnected to said timer for receiving said output signal and calculatingthe speed of said train of conveyor carts.
 6. The apparatus according toclaim 5, further including a transmitter for transmitting an outputsignal representative of the speed of said train of conveyor carts tosaid speed control system.
 7. The apparatus according to claim 4,wherein said speed sensor assembly includes: at least one pair ofproximity switches spaced apart along said track a predetermineddistance from one another for detecting a preselected point on anindividual cart; a timer connected to said switches for measuring theamount of time between when said first proximity switch detects saidpreselected point and when said second proximity switch detects saidpreselected point and providing an output signal representative of saidamount of time; and a speedometer connected to said timer for receivingsaid output signal and calculating the speed of said train of conveyorcarts.
 8. The apparatus according to claim 7, further including atransmitter for transmitting an output signal representative of thespeed of said train of conveyor carts to said speed control system. 9.The apparatus according to claim 4, wherein said conveyor trackincludes: a frame and a pair of spaced apart, generally horizontal,parallel rails attached to said frame.
 10. The apparatus according toclaim 4, wherein each of said conveyor carts includes: a trailer framebase; a roller structure for engaging said conveyor track; a carryingtray for hold objects; and a metal fin hanging downwardly from thebottom of said conveyor cart.
 11. The apparatus according to claim 10,wherein said plurality of selectively energized linear induction motorsdrive said metal fin hanging downwardly from the bottom of said conveyorcart, and said metal fin is moved in the conveyor's line of travel bysaid plurality of selectively energized linear induction motors.
 12. Theapparatus according to claim 4, further including a cart locatingsystem, said system including a light source and a light sensor on aknown cart; and a reflective strip attached to each of a plurality ofpull-down mechanisms, whereby said strip reflects light from said lightsource to said light sensor when said cart is adjacent to each of saidplurality of pull-down mechanisms thereby indicating said known cart isat said known location.
 13. The apparatus according to claim 4, furtherincluding an emergency stopping system, said stopping system includingmeans for reversing the direction of said linear induction motors. 14.The apparatus according to claim 13, wherein said emergency stoppingsystem includes: an activation switch activated by the operator of saidpackage sorting conveyor system; a contactor connected to saidactivation switch for removing power from said plurality of saidselectively energized linear induction motors and for reversing phasesof the power to said plurality of selectively energized linear inductionmotors; and a timer for removing all power to said plurality ofselectively energized linear induction motors after a predetermined timeafter the operator activates said activation switch.